FWP:
Almost the only commentary needed for this verse is a reference to the classic paradox of the lover's life-in-death and death-in-life. Ghalib himself put it as clearly as it could possibly be put, in {219,8}: in love there's 'no difference between death and life', because the lover only 'lives' through seeing the one over whom he would 'die'.
The meaning of kisii par marnaa is not 'to die for someone' in the sense of sacrificing one's life (as in {164,7}), but is more like the idiomatic uses of 'I'm dying for her to notice me' or 'I'm dying for a drink'. I've tried to reflect this distinction by using 'die over' instead of 'die for'.
What kind of a 'life' is it, that's based on dying? And what kind of 'dying' is it, that goes on and on, and recurs again [phir] or repeatedly? Whichever line we look at, we're bounced off a kind of reflective surface of paradox-- back toward the other line, which is equally opaque. Meaning becomes a kind of tennis ball, being volleyed back and forth with no escape in sight.
In particular, it's possible to read the second line, with its impenetrable simplicity, in several ways: (1) the speaker has fallen in love again, so again his life consists of constantly, metaphorically 'dying for' that faithless one; (2) again and again he dies over her, and again and again he finds himself (magically? mystically?) revived, with that very same life restored to him; (3) he keeps dying over her, and that very process of perpetually dying now constitutes his 'life'.
In its extreme structural simplicity this verse is reminiscent of {164,5}, though it's not quite as radical of course.
Compare Mir's take on the paradoxical life-in-death of the lover: M{1069,8}
Nazm:
That is, the one over whom we're dying-- upon seeing that one, we live. (177)
== Nazm page 177